Presently, as a next-generation communication standard of LTE (Long Term Evolution) systems, specifications designed for LTE-Advanced and sophistication thereof are being developed. In LTE-Advanced systems, carrier aggregation (CA) technique is introduced to achieve a higher throughput than that of the LTE systems while ensuring backward compatibility with the LTE systems. In the carrier aggregation, a component carrier (CC) having the maximum bandwidth of 20 MHz supported by the LTE systems is used as a basic component, and it is designed to achieve communication in a broader band by using these multiple component carriers simultaneously.
In the carrier aggregation, user equipment (UE) can use multiple component carriers simultaneously to communicate with abase station (evolved NodeB: eNB). In the carrier aggregation, a highly reliable primary cell (PCell) to ensure connectivity to the user equipment and a secondary cell (SCell) additionally configured for the user equipment during connection to the primary cell are configured. The primary cell is a cell similar to a serving cell in the LTE systems and serves as a cell to ensure connectivity between the user equipment and a network. On the other hand, the secondary cell is a cell configured for the user equipment additionally to the primary cell.
In inter-band carrier aggregation where different frequency bands are simultaneously used, there are cases where influence of harmonics may arise depending on a relative relationship between combinations of frequency bands and frequency positions possessed by operators in these frequency bands. Specifically, the harmonics of a transmission band in a lower-frequency band may fall in a reception band in a higher-frequency band, which may result in sensitivity degradation in the reception band.
In the current LTE standard, it is known that reception sensitivity may degrade for a combination of frequency band 4 (B4) and frequency band 12 (B12) due to the harmonics. In the LTE standard, it is specified that the lower-frequency band 12 is composed of an uplink frequency band (B12 UL) of 699-716 MHz and a downlink frequency band (B12 DL) of 729-746 MHz and the higher-frequency band 4 is composed of an uplink frequency band (B4 UL) of 1710-1755 MHz and a downlink frequency band (B4 DL) of 2110-2155 MHz. For the combination of the frequency band 4 and the frequency band 12, as illustrated in FIG. 1, it is known that a third harmonic arising from transmission in 699-709 MHz in B12 UL may fall in a reception band of 2110-2127 MHz in B4 DL, which may deteriorate the reception sensitivity.
Also, it is known that the reception sensitivity may degrade for a combination of frequency band 3 (B3) and frequency band 8 (B8) due to harmonics. In the LTE standard, it is specified that the lower-frequency band 8 is composed of an uplink frequency band (B8 UL) of 880-915 MHz and a downlink frequency band (B8 DL) of 925-960 MHz and the higher-frequency band 3 is composed of an uplink frequency band (B3 UL) of 1710-1785 MHz and a downlink frequency band (B3 DL) of 1805-1880 MHz. For the combination of the frequency band 3 and the frequency band 8, as illustrated in FIG. 2, it is known that a second harmonic arising from transmission in 905-915 MHz in B8 UL may fall in a reception band of 1810-1830 MHz in B3 DL, which may deteriorate the reception sensitivity.
Currently, a specification based on two patterns is defined for deterioration of the reception sensitivity due to the harmonics. In the first pattern, a low pass filter is inserted in user equipment for measures against the harmonics. The inserted low pass filter cuts the harmonics, and the deterioration of the reception sensitivity in the higher-frequency band is improved. On the other hand, transmission and reception characteristics must be relaxed in compensation. For example, it is assumed that for the combination of the frequency band 4 and the frequency band 12 in the above-stated carrier aggregation, the low pass filter is inserted between a switch and a duplexer for the lower-frequency band 12 in order to cut the harmonics. In the LTE standard, relaxation of the transmission and reception characteristics based on the assumption is designed. Specifically, as illustrated in FIG. 3, a tolerance of the lower bound of the maximum transmission power and reception sensitivity for the frequency band 12 are relaxed. As illustrated, for the combination of the frequency band 4 and the frequency band 12 (CA_4A-12A), the tolerance ΔTIB,c of the lower bound of the maximum transmission power is set to 0.8 dB, and 0.5 dB corresponding to a loss due to the low pass filter is added compared to other tolerances 0.3 dB. Also, in conjunction with the reception sensitivity, for the combination of the frequency band 4 and the frequency band 12 (CA_4A-12A), the reception sensitivity for the frequency band 4 is set to −90 dBm, which is relaxed by 10 dBm from −100 dBm for the case where the low pass filter is not provided. Correspondingly, the communication area is reduced. The first pattern is applied to cases where the sensitivity may degrade due to the harmonics in actual provision of services by an operator such as the case of the combination of the frequency band 4 and the frequency band 12.
On the other hand, in the second pattern, no measure against the harmonics is taken, although the sensitivity may degrade due to the harmonics as stated above. From the standpoint of positions of frequencies possessed by an operator, there are cases where the sensitivity deterioration due to the harmonics is not problematic in actual provision of services by the operator. Accordingly, no measure against the harmonics such as insertion of a low pass filter is taken, and the relaxation of the transmission and reception characteristics as stated above in conjunction with the first pattern is not specified. For example, it is known that for the combination of the frequency band 3 and the frequency band 8 as illustrated in FIG. 2, the second harmonic arising from transmission in 905-915 MHz in B8 UL may fall in a reception band of 1810-1830 MHz in B3 DL. However, no operator uses these two frequency bands, and the relaxation of the transmission and reception characteristics, as defined for the combination of the frequency band 4 and the frequency band 12 as described with reference to FIG. 3, is not currently specified for the combination of the frequency band 3 and the frequency band 8.
In order to implement the inter-band carrier aggregation, for available combinations of frequency bands, user equipment indicates its supported combinations of frequency bands as capability information to a base station, and the base station configures the inter-band carrier aggregation for the user equipment based on the indicated capability information. For example, it is assumed that a combination of the frequency band 1 having the maximum bandwidth 10 MHz and the frequency band 5 having the maximum bandwidth 20 MHz, that is, the combination (CA_1A-5A) of frequency bands having the maximum bandwidth 30 MHz is available in the inter-band carrier aggregation. Meanwhile, the maximum bandwidth (Maximum aggregated bandwidth) supported by the user equipments in the inter-band carrier aggregation may be different depending on terminal types of the user equipments. In the typical LTE system, there may be a mixture of user equipments supporting the maximum bandwidth 30 MHz (Maximum aggregated bandwidth=30 MHz) and user equipments supporting only the maximum bandwidth 20 MHz (Maximum aggregated bandwidth=20 MHz) in the inter-band carrier aggregation. In the LTE system, information element “Bandwidth combination set” is defined to cause the user equipments to indicate supported combinations of frequency bands together with the maximum bandwidth as the capability information.
As illustrated in FIG. 4, if the user equipment supports the combination of the frequency band 1 and the frequency band 5 and has the maximum bandwidth 20 MHz, the user equipment indicates “Bandwidth combination set=0” together with CA_1A-5A as the capability information to the base station. On the other hand, if the user equipment supports the combination of the frequency band 1 and the frequency band 5 and has the maximum bandwidth 30 MHz, the user equipment indicates “Bandwidth combination set=1” together with CA_1A-5A as the capability information to the base station. Upon receiving the capability information, the base station can identify a channel bandwidth (5 MHz, 10 MHz, 15 MHz, 20 MHz or the like) supported by the user equipment based on the received capability information and configure the inter-band carrier aggregation for the user equipment in accordance with the supported channel bandwidth.
Here, “Bandwidth combination set” may be used for not only differentiation among the terminal types of user equipments as stated above but also other applications. For example, when the available channel bandwidth in the inter-band carrier aggregation is changed, “Bandwidth combination set” is used to indicate the changed combination of frequency bands. For example, it is assumed that two “Maximum aggregated bandwidth” items for 30 MHz and 20 MHz are specified for the combination (CA_1A-8A) of the frequency band 1 and the frequency band 8 available in the inter-band carrier aggregation and they are identified with “Bandwidth combination set=0” and “Bandwidth combination set=1”, respectively. Here, as illustrated in FIG. 5, if a channel bandwidth of 3 MHz is newly added to the frequency band 8 for “Maximum aggregated bandwidth” for 30 MHz, “Bandwidth combination set=2” is newly defined for differentiation of the user equipment supporting the channel bandwidth of 3 MHz. In other words, the user equipment supporting the newly added channel bandwidth of 3 MHz indicates “Bandwidth combination set=2” together with CA_1A-8A as the capability information to the base station.
In the LTE system, as illustrated in FIG. 6, “Bandwidth combination set” is indicated in the information element “supportedBandwidthCombinationSet” in the capability information (UE Capability).